1. Field of the Invention
The present invention relates to a paper feeding unit of a printer or a multi-function machine, and more particularly, to a paper insertion limiting device of a paper feeding unit which evenly aligns the front ends of papers when the papers are loaded in the paper feeding unit.
2. Description of the Related Art
In general, an automatic sheet feeder (ASF) is mainly employed in a paper feeding unit in an inkjet printer or a multi-function machine. The ASF is provided with a paper insertion limiting device preventing the front ends of papers from being further inserted beyond a certain position since the papers may come out of the certain position and be inserted into a drive roller when the papers are loaded.
FIG. 1 is a view to illustrate a conventional paper insertion limiting device of a paper feeding unit.
In FIG. 1, the paper insertion limiting device of a paper feeding unit includes a gear cam 10, an elevating plate 20, a sheet regulating lever 30, an elevating spring 40, a pushing plate 50, and a pressing plate 60.
The gear cam 10 is coaxially coupled to an idle gear 72 transmitting power to a pickup roller 70, and a hook 12 is formed to press the sheet regulating lever 30 on one end of the gear cam 10. The idle gear 72 and the gear cam 10 are disposed on the same axis, but constructed to be independently driven. A reference number 71 denotes a pickup gear meshed with the idle gear 72 to rotate the pickup roller 70.
The sheet regulating lever 30 is constructed with a lever shaft 31 rotatably mounted on a printer main body (not shown) in which a paper feeding unit is mounted, a lever arm 34 provided on one end of the lever shaft 31 to be pressed down by the hook 12 of the gear cam 10, and a paper wall 32 preventing the front ends of papers loaded in the paper feeding unit from moving forwards.
The elevating plate 20 is disposed under the sheet regulating lever 30, and one end 21 of the elevating plate 20 is rotatably mounted on the printer main body. The other end of the elevating plate 20 is connected with the elevating spring 40 to keep in contact with the one end of the lever arm 34 of the sheet regulating lever 30 all the time. Further, the middle portion 22 of the other end of the elevating plate 20 has the pushing plate 50 and the pressing plate 60 mounted in order. A paper (not shown) is placed on the upper face of the pressing plate 60.
Descriptions will be made below on the operations of the above conventional paper insertion limiting device of a paper feeding unit.
When a motor (not shown) is driven, a driving force is transferred to the gear cam 10 through the idle gear 72 according to a rotation direction of the motor. When the driving force of the motor is transferred to the gear cam 10, the gear cam 10 rotates so that the hook 12 is released from the lever arm 34. When the hook 12 does not press the lever arm 34, the elevating plate 20 rotates, as indicated by the arrow A in FIG. 1, about the rotation shaft 21 by the elevating spring 40. When the elevating plate 20 rotates upwardly, the sheet regulating lever 30 also rotates upwardly so that the paper wall 32 become tilted at a certain angle. At this time, as the middle portion 22 upwardly pushes the pushing plate 50, the pushing plate 50 upwardly pushes the pressing plate 60 (FIG. 2). When the pressing plate 60 is pushed upwardly, papers loaded on the pressing plate 60 come in close contact with the pickup roller 70. At this state, when the pickup roller 70 rotates, a paper is fed by a friction force between the pickup roller 70 and the papers to a drive roller with no interference of the paper wall 32.
When the paper is completely fed, the gear cam 10 rotates again so that the hook 12 presses the lever arm 34 of the sheet regulating lever 30. When the lever arm 34 is pressed, the sheet regulating lever 30 rotates downwardly so that the paper wall 32 returns to its original position to form a right angle (90 degrees) with the face of the loaded papers. Further, when the lever arm 34 is pressed, the elevating plate 20 positioned under the lever arm 34 is also pressed down so that the elevating plate 20 rotates downwardly to its original position with the elevating spring 40 expanded. Thereafter, the pushing plate 50 and the pressing plate 60 rotate downwardly by weight of their own to their original positions so that the pickup roller 70 and the papers fall apart from each other. That is, when the paper wall 3 is tilted by a certain angle from a right angle by the rotations of the gear cam 10, the papers and the pickup roller 70 come in contact with each other thereby feeding a paper, and, when the gear cam 10 rotates more, the paper wall 32 returns to be at a right angle to a paper to block the front ends of the papers so that the papers loaded in the paper feeding unit are prevented from being inserted into the drive roller.
However, the above paper insertion limiting device of a paper feed unit has various problems as follows.
First, since such paper insertion limiting device has a complicated structure and lots of parts, the manufacturing costs are high. Second, noise is produced since the elevating plate repeats its ascent and descent operations every time a paper is picked up. Third, a paper-sliding prevention member is positively necessary since the papers loaded on the pressing plate are easily slid back with the repetitive ascent and descent of the pressing plate. Fourth, the reliability on paper pickup operations is degraded since the paper pickup condition is not the same all the time.